Text

Rev 2 to Vogtle Units 1 & 2 Spent Fuel Rack Criticality Analysis W/Credit for Soluble Boron
	ML20217H912
Person / Time
Site:	Vogtle
Issue date:	08/31/1997
From:	Fecteau M, Robinson K, Srinilta S; WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:	;
Shared Package
ML20217H901	List: ML20217H898; ML20217H905; ML20217H912; ML20217H924;
References
	WCAP-14720, WCAP-14720-R02, WCAP-14720-R2, NUDOCS 9708130345
	Download: ML20217H912 (65)
	v • d • e

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WESTINGHOUSE NON PROPRIETARY CLASS 3 WCAP-14720, Rev.2 Vogtle Units 1 and 2 Spent Fuel Rack Criticality Analysis With Credit for Soluble Boron August 1997 M. M. Baker S. K. Kapil J. R. Lesko R. N. Milanova K. R. Robinson J. R. Secker T. R. Wathey Prepared : #<%

K. R. Robinson Criticality Services Team f

Verified: / ru k,

/

S. Srinilta 7 j{/ /

Criticality S Yv $pTe_am Approved: [/

The original version of the criticality report used the original WOG methodology which was not approved for use due to comments by the NRC CRGR. Revision 1 of this report reflected the

current NRC approved methodology in WCAP-14416-NP A Revision 1. Revision 2 of this report is being revised to update Figure 8 on page 71 to be consistent with the data in Table 7 for the all cell configuration.

J 4

1

Table of Contents 1.0 Introduction........................................................................................................

-1,1 Des ign Descri pti on.. .. . . . .. . . .. . .. . . . .. . . . . .. . . . .. . . .. . . . . . .. .. . . . . . . . . . .

1.2 Da i gn C ri t eri a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... ._ .3 . . . . . . . . . . . . .

2.0 A n a ly t i cal M e t h od s ... . ......... ................................. .......................................... 5

- 3.0 Criticality Analysis of Unit 1 All Cell Storage... .............................. ................. 6 3.1 No Sol uble Boron 95/95 K,g Calculation ................................................................ 6 3.2 Soluble Boron Credit K,g Calculations .................................................................... 8 3.3 Bumup Credit Reactivity Equivaleneing ..... .. ............ .......................... ................. 9 4.0 Criticality Analysis of Unit 13-out-of-4 Storage............................. . ..............11 4.1 No Soluble Boron 95/95 K ge Calculation ............... ................................................. I 1 4.2 Soluble Boron Credit K,g Cal:ulations .......... .......... .. ................................ ....... ..13

- 4.3 Bumup Credit Reactivity Equivalencing ............. ........ . .. ........... ..... ........ ...........14 5.0 Criticality Analysis of Unit 1 2-out-of-4 Storage.................. .. ........................I 6 5.1 No Soluble Boron 95/95 K g Calculation ......... .......................... ................. .......... I 6 e

5.2 Soluble Boron Credit K,g Calculations .................................................................... 18 6.0 Criticality Analysis of Unit 2 All Cell Storage.......................... .......................... 20 6.I No Soluble Boron 95/95 K g e Calculation ........................................ ........... ........... 2 0 6.2 Soluble Boron Credit K eg Calculations........... ............................................ ........... 22 6.3 Bumup Credit Reactivity Equivalencing .................................................................. 23 7.0 . Criticality Analysis of Unit 2 3-out-of-4 Storage.................. ....................... .... 25 7.1 No Soluble Boron 95/95 K g e Calculation ....................... ..... .............. ................... 25

- 7.2 Soluble Boron Credit K ge Calculations .............. ........................................ . . ....... 2 7 7.3 - B urnup Credit Reactivity Equivalencing ...................................................... .,,........ 28 8.0 Criticality Analysis of Unit 2 2-out-of-4 Storage......................... ............. .. .... 30 8.1 No Soluble Baron 95/95 K g e Calculation ......................... ............ ........... ............. 3 0 8.2 Soluble Boron Credit K,g Calculations..................................................... .............. 32 9.0 Criticality Analysis of Unit 2 3 x3 Checkerboa rd................................................. 34 9.I No Soluble Boron 95/95 K eg Calculation ............................................... .... ........... 34 9.2 Soluble Boron Credit K,g Calculations ........................... ........................................ 3 6 9.3 Bumup Credit Reactivity Equivalencing ...... .. ......................... .............................. 3 7 9.4 IFB A Credit Reactivity Equivalencing ............................................. ........... ........ .. 3 8 9A1 Infinite Multiplication Factor.................................................... ....... ........... 3 9 10.0 Fuel Rod Storage Canister Criticality........... ........ .............. ......... .. . .. 41 11.0 Discussion o f Postulated Accidents............. ............................ .. ..................... 4 2 12.0 Sol u ble Bo ro n C redi t S u m m a ry .................. ............ ............................ ......... 44 Vogtle Units I and 2 Spent Fuel Racks i

13.0 Storage Configu ration In terIace Requlrements................................................... 45 13.1 interface Requirements within Vogtle Racks .... ....... ..... . .. .... ......... .... ... . . ..... . 46 14.0 S u m m u ry o f C ri ticali ty R es ul t s ............................................................................,,4 g Ill b i l o g ra p h y . .......... . . ... . . .. ... . . . . . .. . .. . .... .. .. .. ... ..... .. . . . . .. . . . ... .. . . . . ... .. . .. ... . .. . .. . . . ..... .. . . .... . .. 7 9 11 J

List of Tables:

. Table 1. L Nominal Fuel Parameters Employed in the Criticality Analysis........................ 51 Table 2. All Cell Storage 95/95 Ke g for Vogt!e Unit 1.....................................................52 Table 3. Minimum Burnup Requirements for Vogtle Unit 1............................................ 53 Table -1 -3;out-of 4 Checkerboard 95/95 Ke g for Vogtie Unit 1..................................... . 54 Table 5. 2 out-of-4 Checkerboard 95/95 K g for Vogtle Unit e 1....................................... 55

. Table 6. - All Cell Storage 95/95_ K e g for Vogtie Unit 2 ................. .................................. 56 Table 7. Minimum Bumup Requirements for Vogtle Unit 2............................................ 57 Table S. 3 out-of-4 Checkerboard 95/95 Keg for Vogt!e Unit 2 ...................................... 58 Table 9, 2 out-of-4 Checkerboard 95/95 K g for Vogtie Unit 2 ...................................... 59 e

Table 10. 3x3 Checkerboard 95/95 Ke g for Vogtle Unit 2.................................................,60 Table i1. Minimum IFBA Requirement for the Center Assembly in Vogtle Unit 2 3x3 Checkerboard Storage..................................................... 61 -

Table 12. Postulated Accident Summary for Vogtle Units 1 and 2.................................... 62

~

Table 13. Summary of Soluble Boron Credit Requirements for Vogtle Units 1 and 2...... 63 8

i Vogtle Units 1 and 2 Spent Fuel Racks lii a

List of Figures Figure 1.

Vogtle Unit 1 Spent Fuel Storage Cell Nominal Dimensions ... . .... ...... .. .. .... 64 (

Figure 2. Vogtle Unit 2 Spent Fuel Storage Cell Nominal Dimensions . ............ .. .. ... 65 Figure 3.

Vogtle Unit 2 Rack Module A 5 Limiting Water Gaps and Equivalent Cell... . 66 Figure 4. Vogtle Unit 1 Bumup Ciedit Requirements for All Cell Storage......... ......... .. 67 Figure 5. Vogtle Unit 1 Burnup Credit Requirements for 3-Out-Of-4 Checkerboard Storage............................................................................................68 Figure 6.

Vogtle Units 1 and 2 Empty Cell Checkerboard Storage Configurations ... ..... 69 Figure 7. Vogtle Unit 2 3x3 Checkerboard Storage Configuration . .......... ...... ....... ..... 70 Figure 8. Vogtle Unit 2 Burnup Credit Requirements for All Cell Storage.. .. .......... ...... 71 Figure 9. Vogtle Unit 2 Burnup Credit Requirements for 3-Out-Of-4 Checkerboard Storage.................................................................................................72 Figure 10. Vogtle Unit 2 Burnup Credit Requirements for 3x3 Checkerboard Storage...... 73 Figure 11. Vogtle Unit 2 3x3 Checkerboard IFBA Requirement for Center Assembly. .. .,74 Figure 12. Vogtle Units I and 2 Interface Requirements l

(All Cell to Checkerboard Storage). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Figure 13. Vogtle Units 1 and 2 Interface Requirements (Checkerboard Storage Interface)... . . . . . . . . . . . . . . . . . . . . . . . . . . ..............76 l Figure 14. Vogtle Unit 2 Interface Requirements (3 x3 Checkerboard to All Cell Storage) . . ........ ........ ................ .... ... . .... 77 Figure 15. Vogtle Unit 2 Interface Reciuirements (3x3 to Empty Cell Checkerboard Storage).... .. ........ . ... . ............. ... . . .. 78 Vogile Units 1 and 2 Spent Fuel Racks iv

1.0 Introduction This report presents the results of a criticality analysis of the Vogtle Units I and 2 spent fuel storage racks with credit for spent fuel pool soluble boron. The methodology employed here is contamed in the topical report, " Westinghouse Spent Fuel Rack Criticality Analysis Methodology"m The Vogtle Units 1 and 2 spent fuel racks have been reanalyzed to allow storage of Westinghouse 17x17 fuel assemblies with nominal (design) enriclunents up to 5.00 w/o 235 U in the storage cell locations using credit for checkerboard configurations, burnup credit, and Integral Fuel Bumable Absorber (IFBA)(2) credit. The nominal fuel enrichment for the region is the enrichment of the fuel ordered from the manufacturer. This analysis does not take any credit for the presence of the spent fuel rack Boraflex poison panels. The following storage configurations and enrichment limits were considered in this analysis:

l Unit 1 Enrichment Limits All Cell Storage Storage of 17x17 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1,79 w/o 235 U or satisfy a minimum bumup requirement for higher initial enrichments. The soluble boron concentration that results in a 1(g of less than 0.95 was calculated as 450 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 950 ppm.

3-out-of-4 Storage of 17x17 fuel assemblies in a 3 out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an Storage initial nominal enrichment no greater than 2.45 w/o 235U or satisfy a minimum burnup requirement for higher initial enrichments. A 3-out-of-4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble boron concentration that results in a Ke g ofless than 0.95 was calculated as 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 950 ppm.

2-out-of-4 Storage of 17x17 fuel assemblies in a 2-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an Storage initial nominal enrichment no greater than 5.00 w/o 235U. A 2-out-of-4 checkerboard with empty cehs means that no 2 fuel assemblies may be stored face adjacent. Fuel assemblies may be stored corner adjacent. The soluble boron concentration that results in a K eg of less than 0.95 was calculated as 100 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 1150 ppm.

Introduction 1

-j

Unit 2 Enrichment Limits All Cell Storage Storage of 17xl_7 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1,77 w/o 235 U or satisfy a minimum burnup requirement for higher initial enrichments. The soluble boron concentration that results in a K.gofless than 0.95 was calculated as 350 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 850 ppm.

3-out-of-4 Storage of 17x17 fuel assemblies in a 3-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an Storage initial nominal enrichment no greater than 2.40 w/o 235 U or satisfy a minimum burnup requirement for higher initial enrichments. A 3-out-of4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble boron concentration that results in a K,g ofless than 0.95 was calculated as 350 ppm. Including accidents /the soluble boron credit required for this storage configuration is 1050 ppm.

2-out-of4 Storage of 17x17 fuel assemblies in a 2-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an Storage initial aominal enrichment no greater than 5.00 w/o 235U. A 2-out-of-4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent. Fuel assemblies may be stored comer adjacent. The soluble boron concentration that results in a R eg of less than 0.95 was calculated as 50 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 1250 ppm.

3x3 Checkerboard Storage of Westinghouse 17x17 fuel assemblies with nominal Storage enrichments no greater than 3.20 w/o 235 U (up to 5.00 w/o 235 U with IFBA credit) in the center of a 3x3 checkerboard. The surrounding fuel assemblies must have an initial nominal enrichment no greater than 1.48 w/o 235 U or satisfy a minimum bumup requirement for higher initial enriclunents. Alternatively, the center (high enrichment) cell of the 3x3 checkerboard may be loaded with any assembly which meets a maximum infinite multiplication factor (K ) value of 1.410 at cold reactor core conditions. The soluble boron concentration that results in a K,g ofless than 0.95 was calculated as 500 ppm. Including accidents, soluble boron credit required for this storage configuration is 1050 ppm.

Introduction 2

The Vogtle Units 1 and 2 spent fuel rack analysis is based on maintaining K,g < l.0 including uncertainties and tolerances on a 95/95 basis without the presence of any soluble boron in the i

storage pool (No Soluble Boron 95/95 K,g condition). Soluble boron credit is used :o provide safety margin by maintaining K,g s 0.95 including uncertainties, tolerances, and accident conditions in the presence of spent fuel pool soluble boron. !

l 1.1 Design Description i

t' The Vogtle Unit I spent fuel storage cell is shown in Figure 1 on page 64 and the Vogtle Unit 2 spent fuel storage cell is shown in Figure 2 on page 65 with nominal dimensions provided in each figure.

l The fue! parameters relevant to this analysis are given in Table 1 on page $1. The fuel rod, guide i tube and instmmentation tube claddings are modeled with zircaloy in this analysis. This is consenttive with respect to the Westinghouse ZlRLO product which is a zirconium alloy l containing additional elements including niobium. Niobium has a small absorption cross section I

which causes more neutron capture in the cladding regions resulting in a lower Therefore, this analysis is conservative with respect to fuel e .iblies containing ZIRLOT cladding in fuel rods, guide tubes, and the instumentatic . oe. Results are presented for l

i whichever fuel type,17x17 STANDARD (STD) or 17x17 Optimized Fuel Assembly (OFA), is bounding for a particular storage configuration. With the conservative assumptions of the analyses (e.g. grids are not modeled),17x17 VANTAGE.5H (V5H) fuel asserr.blies provide equivalent i reactivity to 17x17 STD fuel assemblies and 17x17 VANTAGE-5 (VS) fbel assemblies provide j equivalent reactivity to 17x17 OFA fuel assemblies.

The Vogtle Unit 2 spent fuel storage contains as built serage racks which are not consistent with the nominal dimensions provided in Figure 2. Specifically, the as built spacing between storage cells is not consistent with the nominal spacing between storage cells. A criticality analysisW was -

previously performed to address the inconsistencies between the nominal stocage tack cell water .

gap spacing and as built storage rack cell water gap spacings. Based on data from the previous !

l analysis, the as built water gap spacings of rack module A 5 were determined to uound all the l rack modules in the Vogtle Unit 2 spent fuel pool. The limiting water gap spacings for the worst case 3x3 array of cells in rack module A 5 is shown in Figure 3 on page 66. The criticality analysis for the Vogtle Unit 2 all cell,3 out of 4 checkerboard and 2 out of 4. checkerboard configurations was based on an equivalent cell pit 6 which yields a reactivity equivalent to or slightly conservative relative to the reactivity of the as-baitt 3x3 array in rack module A 5 with the

, worst combination of water gap spacings. For the 3x3 comiguration, the cell pitch is based on the

! ' average minimum water gap spacing for the limiting 3x3 array of rack cells in rack module A 5 l which yields a slightly conservative rack reactivity. The cell models used as the basis for the calculations of reactivity in the Vogtle Unit 2 spent fuel racks can be seen in Figure 3 on page 66.

. 12. Design Criteria j Criticality of fuel assemblies in a fuel storage rack is prevented by the design of the rack which 4

limits ruel assembly interaction. This is done by fixing the minimum separation between fuel.

- assemblies and controlling the placement of assemblies into selected storage cells.

i Introduction 3

in this report, the reactivity of the spent fuel rack is analyzed such that K,g remains less than 1.0 under No Soluble lloron 95/95 K,g co.1ditions as defmed in Reference 1. To provide safety !

margin in the criticality analysis of the spent fuel racks, credit is taken for the soluble boron present in the Yogtle Unit I and 2 spent fuel pool. This parameter provides significant negative reactivity in the criticality analysis of the spent fuel rack and will be used here in conjunction with j

administrative controls to ofTset the reactivity increase when ignoring the presence of the spent.

fuel rack lloraflex poison panels. Soluble boron credit provides sufficient relaxation in the enrichment limits of the spent fuel racks.

The design basis for preventing criticality outside the reactor is that, including uncertainties, there e

is a 95 percent probability at a 95 percent confidence level that the effective neutron multiplication factor, K,g, of the fuel rack array will be less than or equal to 0.95.

I I

Introduction 4

2.0 Analytical Methods The criticality calculation method and cross section values are verified by comparison with critical esperiment data for fuel assemblies similar to those for which the racks are designed. This benchmarking data is sufliciently divene to establish that the method bias and uncertainty will apply to rack conditions which include strong neutron absorbers, large water gaps, low moderator densities and spent fuel pool soluble boron.

The design method which insures the criticality safety of fuel assemblies in the fuel storage rack is described in detail in the Westinghouse Spent Fuel Rack Criticality Analysis Methodology t

topical report u. This report describes the computer codes, benchmarking, and methodology which are used to calculate the criticality safety limits presented in this report for Vogtle Units I and 2.

As determined in the benchmarking in the topical report, the method bias using the described methodology of NITAWL.ll, XSDRNpM.S and RENO.Va is 0.00770 AK with a 95 percent probability at a 95 percent confidence level uncertainty on the bias of 0.00300 AK. These values will be used in this report.

Analytical .\lethods 5

3.0 Criticality Analysis of Unit 1 All Cell Storage This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the stoinge of fuelin all cells of the Vogtle Unit I spent fuel storage racks.

Section 3.1 describes the no soluble boron 95/95 K,g KENO Va calculations. Section 3.2 discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations. Finally, Section 3.3 presents the results of calculations perfomied to show the minimum burnup i

requirements for assemblies with initial enrichments above those determined in Section 3.1.

3.1 No Soluble Boron 95/95 Ke g Calculation To determine the enrichment required to maintain K,g < l.0, RENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A final 95/95 Keg is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Ya reference reactivity. The equation for determining the f nal 95 95 K,gis defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,g KENO-Va model for storage of fuel assemblies in all cells of the Vogtle Unit I spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 STD fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 STD fuel assembly design is more reactive than the Westinghouse 17xl 7 OFA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enriclunent of 1.79 w/o 2MU over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing i fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption resuhs in either equivalent or conse Tative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

5. No credit is taken for any 234 U or 236U in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. Ne credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

Criticality Analysis of Unit 1 All Cell Storage 6

9. The moderator3 is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm'em is used.

10. The anay is infmite in the lateral (x and y) extent and fmite in the axial (vertical) extent.

3

11. All available storage cells are loaded with symmetrically positioned (centered within tb storage cell) fuel assemblies.

With the above assumptions, the KENO Va calculations of K,g under nominal conditions resulted in a Keg of 0.94250, as shown in Table 2 on page 52.

l Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 1.0 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

- To evaluate the reactivity etTects of possible variations in material characteristics and mechanical! construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit i spent fuel rack all cell storage configuration, UO 2material tolerances were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methooology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity elTect of asymtretric assembly positioning within the storage cells, KENO Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

1 235 ] Enrichment: The standard DOE enrichment tolerance 235 of10.05 U aboutw/othe nominal reference enrichment of 1.79 w/o 235 U was considered.

00 Density:

2 A 2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishingt A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell 1.D.: The +0.050! 0.025 inch tolerance about the nominal 8.80 inch teference cell 1.D. was considered.

Storage Cell Pitch: The +0.00!-0.320 inch tolerance about the nominal 10.60 inch reference cell pitch was considered.

Stainless Sieel Wall Thickness: The i0.015 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of the four fuel assemblies were positioned together. This reactivity increase was considered.

Criticahty Analysis of Unit 1 All Cell Storage 7

Calculation Uncertaintyt The 95 percent probability /95 percent confidence level uncensinty on the KENO Va nominal reference K,g was considered.

Methodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse RENO Va methodology was considered.

The 95/95 Ke g for the Vogtle Unit I spent fuel rack all cell storage configuration is developed by adding the ternperature and methodology biases and the statistical sum ofindependent tolerances and uncertainties to the nominal KENO Va reference reactivity. The summation is shown in l Table 2 on page $2 and results in a 95/95 K,g of 0.99784.

Since K,n is less than 1.0, the Vogtle Unit I spent fuel racks will remain suberitical when all cells are loaded with 1.79 w/o 235 U 17xl7 fuel assemblies and no soluble boron is present in the spent fuel pool water. In the next section, soluble boion credit will be used to provide safety margin by detennining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncenainties.

3.2 Soluble Boron Credit Kg Calculations To detennine the amount of soluble boron required to maintain K,g s 0.95, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a nonnal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncensinties and summing this term with the temperature and method biases and the nominal KENO-Va reference reactivity.

The assumptions used to develop the nominal case KENO Va model for soluble boron credit for all cell storage in the Vogtle Unit I spent fuel racks are similar to those in Section 3.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 200 ppm soluble boron.

With the above assumptions, the KENO Va calculation for the nominal case with 200 ppm soluble boron in the moderator resulted in a K,g of 0.88054.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,g limit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the etTect of the normal range of spent fuel pool water temperatures (50'F to 185'F). !

To evaluate the reactivity etTects of possible variations in material characteristics and mechanicaFeonstruction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit I spent fuel rack all cell storage configuration, UO 2material tolerances were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology Criticality Analysis of Unit 1 All Cell Storage 8

accuraev were also considered in the statistical summation of uncenainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells,

- KENO Ya calculations were perfonned.

The same tolerance and uncenainty components as in the No Soluble Boron case were considered in the total gertainty statistical summation.

The 95/95 K,gis developed by adding the temperature and methodology biasea and the statistical sum ofindependent tolerances and uncertainties to the nominal KENONa reference reactivity.

The summation is shown in Table 2 on page 52 and results in a 95/95 K,gof 0.93457. i Since K,g is less than or equal to 0.95 including soluble boron credit and uneenainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for all cell storage of ;

17x17 fuel assemblies in the Vogtle Unit I spent fuel racks. Storage of fuel assemblies with '

nominal enriclunents no greater than 1.79 w/o 235 U is acceptable in all cells including the presence of 200 ppm soluble boron.

3.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.79 w/o 235U in all cells of the t Vogtle Unit I spent fuel racks is achievable by means of burnup credit using reactivity l equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease ,

associated with fuel depletion. For burnup credit, a series of reactivityealculations is performed to generate a set of enrichment fuel assembly discharge bumup ordered pairs which all yield an '

equivalent K,g when stored in the spent fuel storage racks.

i j Figure 4 on page 67 shows the constant K,g contours generated for all cell storage in the Vogtle

Unit I spent fuel racks. The curve of Figure 4 represents combinations of fuel enrichment and -

+-

discharge bumup which yield a conservative rack multiplication factor (K:g) as compared to the rack loaded with 1,79 w/o 235 U Westinghouse 17x17 STD fuel assemblies at zero bumup in all

{

! cell locations. The 17x17 STD fuel assembly design provides a conservative reactivity relative to

the 17x17 OFA design at all enrichment and bumup combinations shown in Figure 4 for the curve.

I Uncenainties associated with bumup credit include a reactivity uncertainty of 0.01 AK at j 30,000 MWD /MTU applied linearly to the bumup credit requirement to account for calculation

)

and depletion uncenainties and 5% on the calculated bumup to account for burnup measurement

. uncertcinty, The amount of additional soluble boron needed to account for these uncensinties in j the bumuh requirement of Figure 4 was 250 ppm. This is additional boron above the 200 ppm

[ required in Section 3.2. This results in a total soluble boron requirement of 450 ppm.

1-4 it is imponant to recognize that the curve in Figure 4 is_ based on calculations of constant rack i reactivity, in this way, the environment of the storage rack and its influence on assembly reactivity l ' is implicitly considered. For convenience, the data from Figure 4 are also provided in Table 3 on

- page 53. Use of linear interpolation between the tabulated values is acceptable since the curve i shown in Figure 4 is approximately linear between the tabulated points.

4 I

, Criticality Analysis of Unit 1 All Cell Storage '9 i

'_.-_.,..,..._...--.-~._.--,---.,m.,_.-,,,...m._.c -_,---------,,--._.--.m,,,,-, _..m-.---... . . - - - ~ . . - , - - - . , , _ , , , , . - - -

Previous evaluations have been performed to quantify axial burnup reactivity etTects and to confirm that the reactivity equivalencing methodology described in Reference 1 results in calculations of conservative bumup credit limits. The effect of axial burnup distribution on assembly reactivity has thus been addressed in the development of the Vogtle Unit I all cell storage burnup credit limit.

1 l

Criticality Analysis of Unit 1 All Cell Storage 10

4.0 Criticality Analysis of Unit 13-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuel in 3 out of 4 cells of the Yogtle t' nit I spent fuel storage racks.

Section 4.1 describes the no soluble boron 95/95 K,g KENO Va calculations. Section 4.2 discusses the results of the spent fuel rack 95/95 Ke g soluble boron credit calculations. Finally, Section 4.3 presents the results of calculations performed to show the minimum burnup requirements for assemblies with initial enrichments above those detennined in Section 4.1.

4.1 No Soluble Boron 95/95 Ke g Calculation To detennine the enrichment required to maintain K,g < l.0, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A final 95/95 Keg is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this temi with the temperature and method biases and the nominal KENO Va reference reactivity. The equation for determining the fmal 95 '95 K,g is defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,g KENO Va model for storage of fuel assemblies in 3 out of-4 cells of the Vogtle Unit I spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 STD fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 STD fuel assembly design is more reactive than the Westinghouse 17x17 OFA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 2.45 w/o :35 U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced e trichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

234

5. No credit is taken for any U or 236 U in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

Criticality Analysis of Unit 13-out-of-4 Storage 11 a

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F A water density of 1.0 gm'em3 is used.

10. The anay is infinite in the lateral (x and y) extent and fmite in the axial (venical) extent, j

i 1. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 3 out of 4 checkerboard arrangement. A 3 out of 4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. Figure 6 on page 69 shows the 3 out-of 4 checkerboard configurations.

With the above assumptions, the RENO Va calculations of K,g under nominal conditions resulted in a R eg of 0.95418, as shown in Table 4 on page 54.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 1.0 K,g limit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse RENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the etTect of the normal range of spent fuel pool water temperatures (50*F to IS$*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit I spent fuel rack 3-out of-4 checkerboard configuration, UO2material tolerances were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

1 35 U Enrichment: The standard DOL enrichment tolerance of 0.05 w/o 235 U about the nominal reference enrichment of 2.45 w/o 23sU was considered.

UO 2Density: A 12.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The +0.050/ 0.025 inch tolerance about the nominal 8.80 inch teference cell 1.D. was considered.

Storage Cell Pitch: The +0.00/--0.320 inch tolerance about the nominal 10.60 inch reference

- cell pitch was considered.

Stainless Steel Wall Thickness: The 0.015 inch tolerance about the nominal 0.075 inch ,

reference stainless steel wall thickness was considered.

Criticality Analysis of Unit 13 out-of 4 Storage 12

l l

Asymmetrie Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of the three fuel assemblies were positioned together. This reactivity increase was considered.

Calculation Uncertah..y: The 95 percent probability /95 percent confidence level uncertainty on the KENO Va nominal reference K,g was considered.

Methodology Uncertaintyt The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

The 95/95 K,g for the Vogtle Unit I spent fuel rack 3-out-of 4 checkerboard configuration is ,

developed by adding the temperature and methodology biases and the statistical sum cf l

independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The i summation is shown in Table 4 and results in a 95/95 K,g of 0.99578.

Since Ke g is less than 1.0, the Vogtle Unit I spent fuel racks will remain suberitical when j

3-out of 4 cells are loaded with 2.45 w/o 235 U 17x17 fuel a.,semblies and no soluble boron is present in the spent fuel pool water, in the next section, soluble boron credit will be used to '

provide safety margin by determining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties.

4.2 Soluble Boron Credit Kg Calculations To determine the amount of soluble boron required to maintain K,g s 0.95, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a nonnal pool temperature range and the effects of material and constmetion tolerance variations.

A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO-Va reference reactivity.

The assumptions used to develop the nominal case KENO Va model for soluble boron credit for 3 out-of-4 cell storage in the Vogtle Unit I spent fuel racks are similar to those in Section 4.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 200 ppm soluble boron.

With the ab'ove assumptions, the KENO Va calculation for the nominal case with 200 ppm soluble boron in the moderator resulted in a Re gof 0.89720.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,glimit. The following biases were included:

Methodology: The benchmarking bias as detennined for the Westinghouse KENO Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the etTect of the normal range of spent fuel pool water temperatures (50'F to 185'F).

Criticality Analysis of Unit 13 out-of 4 Storage 13

-- - = - - . - - - - - _ - - . - - - - - -

i l

To evaluate the reactivity effects of possible variations in materir.1 characteristics and mechanicaliconstruction dimensions, additional P110ENIX P calculations were performed. For the Vogtle Unit I spent fuel rack 3.out of-4 checkerboard configuration, UO material tolerances were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and stainless steel wall thickness. Uncensinties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The same tolerance and uncertainty compcments as in the No Soluble Boron case were considered in the total uncertainty statistical summatiom l

The 95/95 K,g is developed by adding the temperature and methodology biases and the statistical sum ofindependent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 4 on page 54 and results in a 95/95 K,g of 0.93777.

Since 1(g is less than or equal to 0.95 including soluble boron credit and uncenalnties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for 3 out of 4 storage of 17x17 fuel assemblies in the Vogtle Unit I s nominal enrichments no greater than 35 2.45 w/o pent fuel racks. Storage of fuel as U is acceptable in 3 out-of-4 cells including the presence of 200 ppm soluble boron.

4.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblics with initial enrichments higher than 2.45 w/o 235 U in 3-out-of 4 cells of the Vogtle Unit I spent fuel racks is achievable by meana of burnup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For bumup credit, a series of reactivity calculations is performed to generate a set of enrichment fuel assembly discharge bumup ordered pairs which all yield an equivalent }Qg when stored in the spent fuel storage racks.

Figure 5 on page 68 shows the constant Ke g contours generated for 3-out of 4 cell storage in the Vogtle Unit I spent fuel racks. The curve of Figure 5 represents combinations of fuel enrichment and discharge burnup which vield the same rack multiplication factor (K,g) as compared to the rack loaded with 2.45 w/o 2M U Westinghouse 17x17 STD fuel assemblies at zero bumup in 3-out of 4 cell locations. The 17xl7 STD fuel assembly design provides a conservative reactivity relative to the 17x17 0FA design at all enrichment and burnup combinations shown in Figure 5 for the curve.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly to the bumup credit requirement to account for calculation 1 and depletion uncertainties and 5% on the calculated burnup to account for burnup measurement uncertainty. The amount of additional soluble boron needed to account for these uncertainties in the bumup requirement of Figure 5 was 150 ppm. This is additional boron above the 200 ppm required in Section 4.2. This results in a total soluble boron requirement of 350 ppm.

- Criticality Analysis of Unit 13-out-of-4 Storage 14

~

11 is important to recognize that the curve in Figure 5 is based on calculations of constant rack reactivity. In this way, the emironmeat of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 5 are also provided in Table 3 on page 53. Use of linear interpolation between the tabulated values is acceptable since the curve shown in Figure 3 is approximately linear between the tabulated points. !

Previous evaluations have been performed to quantify axial bumup reactivity effects and to ,

confirm that the reactivity equivalencing methodology described in Reference I results in calculations of conservative bumup credit limits. The efTect of axial bumup distribution on J assembly reactivity has thus been addressed in the development of the Vogtle Unit 13 out-of-4

cell storage burnup credit limit, i

l l _

v l

l Criticality Analysis of Unit 13-out-of-4 Storage 15

5.0 Criticality Analysis of Unit 12-out-of-4 Storage This section describes the analytical techniques and models employed to perfonn the criticality analysis for the storage of fuelin 2 out of 4 cells of the Vogtle Unit I spent fuel storage racks.

Section 5.1 describes the no soluble boron 95/95 K,g KENO Va calculations and Section 5.2 1

discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations.

5.1 No Soluble Boron 95/95 Ke rr Calculation To determine the enrichment required to maintain K,g < l.0, KEliO Va is used to establish a nominal reference reactivity and PHOENIX p is used to assess the temperature bias of a normal l pool temperature range and the effects of material and construction tolerance variations. A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal RENO Va reference reactivity. The equation for detennining the final 95/95 K,gis defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,gKENO Va model for storage of fuel assemblies in 2-out of-4 cells of the Vogtle Unit I spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 OFA fuei design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 OFA fuel assembly design is more reactive than the Westinghouse 17x 17 STD fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 5.00 w/o 235 U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

234

5. No credit is taken for any U or 236 U in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

9. The moderator is water with 0 ppm soluble baron at a temperature of 68'F. A water density of 1.0 gm'em3 is used.

10. The arTay is infmite in the lateral (x and y) extent and finite in the axial (vertical) extent.

Criticality Analysis of Unit 12 out-of 4 Storage 16 m

l 11, Tuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 2 out of 4 checkerboard arrangement as shown in Figure 6 on page 69. A 2 out of-4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent.

With the above assumptions, the KENO Va calculations of Re g under nominal conditions resulted 1 a Ke g of 0.93670, as shown in Table 5 on page 55.

remperature and methodology biases must be considered in the final K,g summation prior to comparing against the 1.0 K,glimit. The following biases were included:

Methodologyt The benchmarking bias as determined for the Westinghouse RENO Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the etTect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit I spent fuel rack 2 out of-4 checkerboard configuration, UO2material tolerances were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235 U Enrichment: The standard DOE enrichment tolerance of10.05 w/o 235Uaboutthe nominal reference enriclunent of 5.0 w/o 235 U was considered.

UO 2Density: A i2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The +0.050/-0.025 inch tolerance about the nominal 8.80 inch reference cell 1,D. was considered.

Storage Cell Pitch: The +0.00/-0320 inch tolerance aoout the nominal 10.60 inch reference cell pitch was considered.

Stainless Steel Wall Thickness: The 10.015 in h tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comers of the two fuel assemblies were positioned together. This reactivity increase was considered.

Criticality Analysis of Unit 12-out-of 4 Storage 17

Calculation Uncertaintyt The 95 percent probability /95 percent confidence level uncertainty on the KENO Va nominal reference K,gwas censidered.

Methodology Uncertaintyt The 95 percent probability /95 percent confidence uncertainty in .

the benchmarking bias as detennined for the Westinghouse KENO Va methodology was '

l considered.

1he 95/95 K,g for the Vogtle Unit 1 spent fuel rack 2 out of 4 checkerboard configuration is developed by adding the temperature and methodology biases and the statistical sum of l

independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The summation is shown in Table 5 on page 55 and results in a 95/95 K,g of 0.95741.

Since K,g is less than 1.0, the Vogtle Unit I spent fuel racks will remain suberitical when 2 out of-4 cells are loaded with 5.00 w/o 2nU 17x17 fuel assemblies and no soluble boron is present in the spent fuel pool water, in the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties.

5.2 Soluble Boron Credit Kg Calculations To determine the amount of soluble boron required to maintain K,g s 0.95, KENO Va is used to establish a nominal reference reactivity and PliOENIX P is used to assess the temperature bias of a nonnal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational und methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity.

The assumptions used to develop the nominal case KENO Va model for soluble boron credit for 2 out of 4 cell storage in the Vogtle Unit I spent fuel racks are similar to those in Section 5.1 except for assumption 9 regarding the moderator soluble boron concentration. The modera,or is replaced with water containing 100 ppm soluble boron.

With the above assumptions, the RENO Va calculation for the nominal case results in a Re g of 0.92077.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,g limit. The following biases were included:

Methodology: The benchmarking bias as determiaed for the Westinghouse KENO Va methodology was considered.

Water Temperature: A reactivity bias determined in PliOENIX P was applied to account for the efrect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in msterial characteristics and mechanicaUconstruction dimensions, additional PliOENIX P calculations were performed. For the Vogtle Unit 1 spent fuel rack 2-out of 4 checkerboard configuration, UO material tolerances were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology Criticality Analysis of Unit 12-out-of-4 Storage 18

accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENONa calculations were perfonned.

The same tolerance and uncertainty components as in the No Soluble 11oron case were considered in the to'ai uncertainty statistical summation:

The 95/95 Ke gis developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 5 on page 55 and results in a 95/95 K,gof 0.93835.

Since K,g is less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for 2 out of 4 cell i storage of 17x17 fuel assemblies in the Vogtle Unit 1 spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 5.00 w/o 235 U is acceptable in 2-out-of 4 cells including the presence of 100 ppm soluble boron.

Criticality Analysis of Unit i 2-out of 4 Storage 19

6.0 Criticality Analysis of Unit 2 All Cell Storage i

This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuelin all cells of the Vogtle Unit 2 spent fuel storage racks.

Section 6.1 desenbes the no soluble boron 95/95 K,g RENO Va calculations. Sectior. 6.2 discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations. Finally, Section 6.3 presents the results of calculations performed to show the minimum bumup requirements for assemblies with initial enriclunents above those determined in Section 6.1.

6.1 No Soluble Boron 95/95 Ke rrCalculation To detennine the enriclunent required to maintain K,g < l.0, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A final 95/95 K eg is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal RENO Va reference reactivity. The equation for detennining the fmal 95 95 K,gis defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,g KENO Va model for storage of fuel assemblies in all cells of the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters relevant to the enticality analysis are based on the Westinghouse 17xl7 STD fuel design (see Table 1 on page $1 for fuel parameters),

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 STD fuel assembly design is more reactive than the Westinghouse 17x17 0FA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 1,77 w/o 235 U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Yogtle, including those with annular pellets at the fuel rod ends.

5. No credit is taken for any 2M U or 236U in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

Criticality Analysis of Unit 2 All Cell Storage 20

1 l

9. The moderator 3 is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm em is used.

10. The array is infmite in the lateral (x and y) extent and fmite in the axial (vertical) extent.

I 1. All available storage cells are loaded with fuel assemblics which are symmetrically positioned (centered within the storage cell).

With the above assumptions, the KENO Va calculations of R,g under nominal conditions resulted in a K,g of 0.96819, as shown in Table 6 on page 56.

Temperature and methodology biases must be considered in the final R e g summation prior to comparing against the 1.0 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse RENO Va methodology ns considereu.

Water Temperature: A reactivity bias determined in P110ENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

- To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack all cell storage configuration. UO 2material tolerances were considered along with construction tolerances related to the ce;l I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity etTect of asymmetric assembly positiening within the storage cells, RENO Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235 U Enrichment: The standard DOE enrichment tolerance of 0,05 w/o 235U about the nominal reference enrichment of 1.77 w/o 235U was considered.

UO 2Densityt A 12.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The 0.030 inch tolerance about the nominal 8.75 inch reference cell 1.D.

was considered.

Storage Cell Phth: The 10.040 inch tolerance about the equivalent cell pitch of 10.34 inches was assumed (see Section 1.1 for discussion of equivalent cell)c Stainless Steel Wall Thickness: The 10.005 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comers of the four fuel assemblies were positioned together. This reactivity increase was considered.

Criticality Analysis of Unit 2 All Cell Storage 21

.. .. J

I Calculation Uncertaintyt The 95 percent probability /95 percent confidence level uncertainty on the KENONa nominal reference K,g was considered.

Methodology Uncertaintyt The 95 percent probability /95 percent confidence uneenainty in

] the benchmarking bias as determined for the Westinghouse KENONa methodology was j considered.

1 The 95/95 Reg for the Vogtle Unit 2 spent fuel tack all cell storage configuratiot, is developed by

adding the temperature and methodology biases and the statistical sum ofindependent tolerances

1 and uncertainties to the nominal KENONa reference react!vity. The summation is shown in Table 6 and results in a 95/95 K,gof 0.99851.

Since K,gis less than 1.0 gthe Vogtle Unit 2 spent fuel racks will remain suberitical when all cells are loaded with 1.77 w/o *MU 17x17 fuel assemblies and no soluble boron is present in the spent fuel pool water, in the next section soluble boron credit will be used to provide safety margin b) - ,

determining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties.

6.2 Soluble Boron Credit Kg Calculations To determine the amount of soluble boron required to maintain K,g s 0,95, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K gis e developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal RENONa reference reactivity.

The assumptions used to develop the nominal case KENONa model for soluble boron credit for all cell storage in the Vogtle Unit 2. pent fuel racks are similar to those m Section 6.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 150 ppm soluble boron.

With the above assumptions, the KENONa cal:ulation for the nominal case with 150 ppm soluble boron in the moderator resulted in a K,gof 0.92003.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,g limit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENONa methodology was considered.

Water Temperature: .A reactivity bias determined in PHOENIX P was applied to account for the efTect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For.

the Vogtle Unit 2 spent fuel rack all cell storage configuration. UO2 material tolerances were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and

- stainless steel wall thickness. Uncertainties associated with calculation and methodology Criticality Analysis of Unit 2 All Cell Storage 22

accuracy wcre also considered in the statistical summation of uncenainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KESO.% calculations were perfonned.

The same tolerance and uncertainty components as in the No Soluble Boron case were considered l in the total uncertainty statistical sumraation:

The 95 95 K,g is developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 6 on page 56 and results in a 95/95 K,gof 0.94998.

Since K,gis less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for all cell storage of 17xl? fuel assemblies in the Vogtle Unit 2 spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 1.77 w/o 235 U is acceptable in all cells including the presence of 130 ppm soluble boron.

6.3 Ilurnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.77 Co 235 0 in t li cells of the Vogtle Unit 2 spent fuel racks is achievable by means of burnup credit using reactivity equivalencing. The concept of reactivity equivalencing is predierted upon the reactivity decrease associated with fuel depletion. For burnup credit, a series of reactivity calculations is perfonned to generate a set of enrichment fuel assembly discharge bumup ordered pairs which all yield an equivalent K,g when stored in the spent fuel storage racks.

Figure 8 on page 71 shows the constant Ke g contours generated for all cell storage in the Vogtle Unit 2 spent fuel racks. The curve of Figure 8 verresents combinations of fuel enrichment and discharge bumup which vield the same rack muitiplication factor (K,g) as compared to the rack loaded with 1.77 w/o 235 U Westinghouse 17xl7 S'ID fu:1 assemblies at zero burnup in all cell locations. The 17x17 STD fuel assembly design provides a conservative reactivity relative to the 17xl 7 OFA design at all ennehment and bumup combirations shown in Figure 8 for the curve.

Uncertainties associated with burnup credit incluc'e a reactivity uncertainty of 0.01 AK at 30,000 MWDMTU applied linearly to the bumun credit requirement to account for calculation and depletion uncertainties and 5% on the calculated burnup to account for burnup merisurement uncertainty. The amount of additional soluble boron needed to account for these uncertainties in the bumup requirement of Figure 8 wr.s 200 ppm. This is additional boron above the 150 ppm required in Section 6.2. This results in a utal soluble boron requirement of 350 ppm.

It is important to recognize that the curve in Figure 8 is based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 8 are also provided in Table 7 on page 57. I'se oflinear interpolation between the tabulated values is acceptable since the curve shown in Figure 8 is approximately linear between the tabulated points.

Criticality Analysis of Unit 2 All Cell Storage 23

i l

! Previous evaluations have been performed to quantify axial bumup reactivity effects and to j confirm that the reactivity equivalencing methodology described in Reference 1 results in i

calculations of conservative bumup credit limits. The efTect of axial bumup distribution on l assembly reactivity has thus been addressed in the developrnent of the Vogtle Unit 2 all cell l storage bumup credit limit.

l i

l l

I l

l t

(

i 1

l Criticality Analysis of Unit 2 All Cell Storage 24 L. - . . - . - _ .

7.0 Criticality Analysis of Unit 2 3-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuel in 3 out of-4 cells of the Yogtle Unit 2 spent fuel storage racks.

Section 7.1 describes the no soluble boron 95/95 K,g RENO-Va calculations. Section 7.2 discusses the results of the spent fuel rack 95/95 Kett soluble boron credit calculations. Finally, Section 7.3 presents the results of calculations perfonned to show the minimum bumup requirements for assemblics with initial enrichments above those determined in Section 7.1. l

-7.1 No Soluble Boron 95/95 Ke rr Calculation To detennine the enrichment required to maintain Ke g < l.0, KENO Va is used to establish a nominal reference reactivity and PilOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A fmal 95/95 Keg is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity. The equation for determining the final 95'95 K egis defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 Kety KENO-Va model for storage of fuel assemblies in 3 out of-4 cells of the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters reievant to the criticality analysis are based on the Westinghouse 17x17 STD fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17xl7 STD fuel assembly design is more reactive than the Westinghouse 17x17 OFA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 2.40 w/o 235U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

5. No credit is taken for any 234U or:36U in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

Criticality Analysis of Unit 2 3 out-of 4 Storage 25

^

F ,

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm cm3 is used.

10. The array is infmite in the lateral (x and y) extent and finite in the axial (vertical) cxtent.

i 1. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 3 out of-4 checkerboard arrangement. A 3 out-of-4 checkerboard with ernpty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. Figure 6 on page 69 shows the 3 out of-4 checkerboard configurations.

With the above assurnptions, the KENO Va calculations of K eg under nominal conditions resulted in a K,g of 0.97240, as shown in Table 8 on page 58.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 1.0 K,glimit. The following biases were included:

Methodologyt The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

Water Temperaturet A reactivity bias detennined in PilOENIX P was applied to account for the etreet of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack 3 out of 4 checkerboard configuration, UO material tolerances were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed. c The following tolerance and uncenainty components were considered in the total uncertainty statistical summation:

235 U Enrichment: The standard DOE enrichment tolerance of10.05 w/o 235U about the nominal reference enrichment of 2.40 w/o 235U was considered.

UO 2Density: A 2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page SI) was considered, Fuel pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominai dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The 0.030 inch tolerance about the nominal 8.75 inch reference cell 1.D.

was considered.

Storage Cell Pitch: The 10.040 inch tolerance about the equivalent cell pitch of 10.34 inches was assumed (see Section 1.1 for discussion of equivalent cell).

Stninless Steel Wall Thickness: The 0.005 inch tolerance about the nominal 0,075 inch reference stainless steel wall thickness was considered.

Criticality Analysis of Unit 2 3-out-of 4 Storage 26-

a ,

1 4

Ay mmetric Anembly Position: The KENO Ya reference reactivity calculation assumed fuel 1

assemblies were symmetrically positioned (centered) within the storage cells Conservative calculations show that an increase in reactivity can occur if the corners of the three fuel assemblies were positioned together. This reactivity increase was considered.

Calculation Uncertaintyt The 95 percent probability /95 percent confidence level uncertainty j q on the KENO Va nominal reference K,g was considered.

4 '

Methodology Uncertaintyt The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse KENO Va methodology was considered. .

/

The 95/95 K,g for the Vogtle Unit 2 spent fuel rack 3 out of 4 checkerboard configuration is developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The .

summation is shown ;n Table 8 and results in a 95/95 K,g of 0.99464.

4 Since K,g is less than 1.0, the Vogtle Unit 2 spent fuel racks will remain suberitical when a

3 out of 4 cells are loaded with 2.40 w/o *U 17xl7 fuel assemblies and no soluble boron is

present in the spent Ibel pool water. In the next section, soluble boron credit will be used to '

1 provide safety margin by detennining the amount of soluble boron required to maintain K,g s

0.95 including tolerances and uncertainties.

. r

7.2 Soluble Boron Credit Kg Calculations i

To detennine the amount of soluble boron required to maintain K,g s 0.95, KENO Va is used to l establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of

, a nonnal pool temperature range and the effects of material and construction tolerance variations.

1 A final 95/95 K,g is developed by statistically combining the in.iividual tolerance impacts with I

the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity.

1 The assumptions used to develop the nominal case KENO Va model for soluble boron credit for i 3-out of 4 storage in the Vogtle Unit 2 spent fuel racks are similar to those in Section 7.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 200 ppm soluble boron.

With the above assumptions, the KENO Va calculation for the nominal case with 200 ppm soluble -

boron in the moderator resulted in a K,gof 0.91440. i Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

}~

Water Temperaturet A reactivity bias determined in PHOENIX P was applied to account for I the etTect of the normal range of spent fuel pool water temperatures (50'F to 185'F). <

i.

i Criticality Analysis of Unit 2 3-out of-4 Storage 27

To evaluate the reactivity effects of possible variations in material characteristics and mechanical construction dimensions, additional PHOENIX P calculations were perfonned. For the Vogtle Unit 2 spent fuel rack 3 out of-4 checkerboard configuration, UO2n.aterial tolerances were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and stainless steel svell thickness. Uncertainties associated with calculation and methodology accuracy were a so considered in the statistical summation of uncertainty components. To evaluate the reacdvity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The same tolerance and uncenainty components as in the No Soluble Boron case were considered in the total uncenalnty statistical summation:

The 95/95 K,gis developed by adding the temperature and methodology biases and the statistical sum ofladependent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 8 on page 58 and results in a 95/95 K,g of 0.93716.

Since Keg is less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for 3 out of 4 storage of :

17x17 fuel assemblies in the Vogtle Unit 2 s nominal enrichments no greater than 35 2.40 U is w/o ' inpent acceptable 3 outfuel racks.

of 4 cells Storage including the of fuel as 3

presence of 200 ppm soluble boron. i 7.3 Burnup Credit Reactivity Equivalencing .

Storage of fuel assemblies with initial enrichments higher than 2.40 w/o 235 U in 3 out of 4 cells of the Vogtle Unit 2 spent fuel racks is achievable by means of burnup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For bumup credit, a series of reactivity calculations is performed to generate r set of enrichment fuel assembly discharge bumup ordered pairs which all yield an equivalent K,g when stored in the spent fuel storage racks.

Figure 9 on page 72 shows the constant K,g contours generated for 3 out-of 4 storage in the '

Vogtle Unit 2 spent fuel racks. The curve of Figure 9 represents combinations of fuel enrichment and discharge burnup which vield the same rack multiplication factor (K,g) as compared to the rack loaded with 2.40 w/o 238 U Westinghouse 17x17 STD fuel assemblies at zero burnup in 3 out of-4 cell locations. The 17x17 STD fuel assembly design provides a conservative reactivity relative to the 17x17 OFA design at all enrichment and burnup combinations shown in Figure 9 for the curve.

Uncenainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly to the burnup credit requirement to account for calculatior.

and depletion uncenainties and 5% on the calculated bumup to account for burnup measurement uncenainty. The amount of additional soluble boron needed to account for these uncenainties in the bumup requirement of Figure 9 was 150 ppm. This is additional boron above the 200 ppm required in Section 7.2, This results in a total soluble boron requirement of 350 ppm.

Criticality Analysis of Unit 2 3-out-of 4 Storage 28

_ _ _ _ . . _ ~ _._ _ . _ _ ,

l It is important to recognize that the curve in Figure 9 is based on calculations of constant rack i

reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 9 are also provided in Table 7 on page 57. Use of linear interpolation between the tabulated values is acceptable since the curv i

shown in Figure 8 is approximately linear between the tabulated points.

Previous evaluations have been performed to quantify axial bumup reactivity effects and to confirm that the reactivity equivalencing methodology described in Reference I results in calculations of conservative bumup credit limits. The effect of axial bumup distribution on assembly reactivity has thus been addressed in the development of the Vogtle Unit 2 3-out-of 4 cell storage bumup credit limit. l l

l Criticality Analysis of Unit 2 3 out of 4 Storage 29

l l

l 8.6 Criticality. Analysis of Unit 2 2-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality (

analysis for the storage of fuel in 2 out of-4 cells of the Vogtle Unit 2 spent fuel storage racks.

Section 8.1 describes the no soluble boron 95/95 Ke rr KENO Va calculations and Section 8.2 discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations.

8.1 No Soluble Boron 95/95 Ke g Calculation To detennine the enrichment required to maintain K,g < l.0, KENO-Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the efTects of material and construction tolerance variations. A fmal 95/951(g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity. The equation for determining the final 95 95 K,gis defined in Reference 1.

The fbilowing assumptions are used to develop the No Soluble Boron 95/95 K,g KENO Va model for storage of fuel assemblies in 2 out of-4 cells of the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 OFA fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 OFA fuel assembly design is more reactive than the Westinghouse 17x17 STD fuel assembly design.

2. Fuel assemblies contain uranium dioxih at a nominal enrichment of 5.00 w/o 235U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rA ends.

5. No credit is taken for any 23dU or :36U in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any burnable absorber in the fuel rods.

S. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Bonflex volume is replaced with water.

9. The moderator is water with 0 ppm soluble boron at a temperature of 6S'F. A water densit/ of 1.0 gm/cm3 is used.

10. The array is infinite in the lateral (x and y) extent and finite in the axial (vertical) extent.

Criticahty Analysis of Unit 2 2-out-of-4 Storage 30

f qt

i. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 2-out of-4 checkerboard arrangement as sbown in Figure 6 on page 69, A 2 out of-4 checkerboard with empty cells means that no 2 fuel assembli' . may he stored face i adjacent.

With the above assumptions, the KENP Va calculations of Ke gunder nominal conditions resulted

] in a K egof 0,94622, as shown in Table 9 on page 59.

l Temperature and methodology biases must be considered in the final K,g summation prior to

comparing against the 1.0 K,glimit. The following biases were included

1 Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was ennsidered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for 3 ti:e effect of the normal range of spent fuel pool water temperatures (30*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For 4

the Vogtle Unit 2 spent fuel rack 2-out-of-4 checkerboard configuration, UO2material tolerances were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncenainties associated with calculation and methodology i;

accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells,

] KENO Va calculations were performed.

J l The following tolerance and uncertainty components were considered in the total uncertainty 1

statistical sunynation:

! 235 U Enrichment: The standard DOE enrichment tolerance of10.05 w/o 235U about the

! nominal referenct un ent of 5.0 w/o 235 U was considered, s

UO Density: A 2.R varianon about the nominal reference th:oretical density (tha nominal reference values are listed in Table 1 on page 31) was considered.

Fuel Peilet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal

dishing (tM nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The 0.030 inch tolerance about the nominal 8.75 inch reference cell I.D.

, was considered.

Storage Cell Pitch: be 0.040 inch tolerance about the equivalent cell pitch of 10.34 inches L was assumed. (see Section 1.1 for discussion of equivalent cell).

Stainless Steel Wall Thickness: The 0.005 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of the two fuel assemblies were positioned together. This reactivity increase was considered.

Criticality Analysis of Unit 2 2-out-of-4 Storage 31

d Calculation Uncertainty: The 95 percert probability /95 racent u nfidance level uncertainty on the RENO-Va nominal reference K eg was considered.

Alethodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse RENO-Va methodology was considered.

l The 9555 K eg for the Vogtle Unit 2 spent fuel rack 2-out-of-4 checkerboard configuration is 3

developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncettainties to the nominal KENO-Va reference reactivity. The

summation is shown in Table 9 on page 59 and results in a 95/95 Ke gof 0.96067.

-Since Ke g is less than 1.0, the Vogtle Unit 2 spent fuel racks will remain suberitical when i

2-out of-4 cells are loaded with 5.0 w/o 235 U 17x17 fuel assemblies and no soluble boron is

, present in the spent fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain Ke g s 0.95 including tolerances and uncertainties.

1 8.2 Soluble Boron Credit Keg Calculations To determine the amount of soluble boron required to maintain Ke g s 0.95, KENO-Va is used to establish a nominal reference reactivity and PHOENIX-P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations.

A fmal 95/95 K,g is developed by statistically combining the individual tolerance impacts with

. e calculational and methodology uncertainties and summing this term with the temperature and

, raethod biases and the nominal KENO-Va reference reactivity.

The assumptions used to develop the nominal case RENO-Va model for soluble boron credit for 4

2-out-of-4 storage in the Vogtle Unit 2 spent fuel racks are similar to those in Section 8.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 50 ppm soluble boron.

I With the above assumptions, the KENO-Va calculation for the nominal case results in a Ke g of

, 0.93390.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 0.95 Ke glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and

mechanicaUconstruction dimensions, additional PHOENIX-P calculations were performed. For the Vogtle Unit 2 spent fuel rack 2-out of-4 checkerboard configuration, UO2material tolerances were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology Criticality Analysis of Unit 2 2-out-of-4 Storage 32

1 accuracy were also considered in the statistical summation of uncertainty components. To l evaluate the reactivity effect of asymmetric assembly positioning within the storage cells KENONa calculations were performed.

The same tolerance and uncertainty components as in the No Soluble Boron case were considered

- in the total uncertainty statistical summation:

The 95'95 K egis developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO-Va reference reactivity.

The summation is shown in Table 9 on page 59 and results in a 95/95 K,gof 0.94737.

I Since Keg is less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for 2-out-of-4 cell storage of 17x17 fuel assemblies in the Vogtle Unit 2 spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 5.0 w/o 235 U is acceptable in 2-out-of-4 cells including

, the presence of 50 ppm soluble boron.

4 d

4 i

(

A.

Criticality Analysis of Unit 2 2-out-of-4 Storage 33

9.0 Criticality Analysis of Unit 2 3x3 Checkerboard This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuel in a 3x3 checkerboard in the Vogtle Unit 2 spent fuel storage racks.

Section 9.1 describes the no soluble boron 95/95 K eg KENO-Va calculations. Section 9.2 discusses the results of the spent fuel rack 95/95 Ke g soluble boron credit calculations. Section 9.3 presents the results of calculations performed to show the minimum bumup requirements for the eight peripheral assemblies with initial enrichments above those determined in Section 9.1.

Section 9.4 presents the results of calculations performed to show the minimum IFBA requirements for enrichments greater than 3.20 w/o 235 U in the center assembly of the 3x3 checkerboard. Finally Section 9.4.1 discusses the infmite multiplication factor.

9.1 No Soluble Boron 95/95 Ke g Calculation To determine the enrichment required to maintain Ke g < l.0, K.ENO Va is used to establish a nominal reference reactivity and PHOENIX-P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A fmal 95/95 Keg is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and sununing this term with the temperature and method biases and the nominal KENO-Va reference reactivity. The equation for determining the final 95/95 K,g is defmed in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,tr KENO Va model for storage of fuel assemblies in a 3x3 checkerboard in the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 STD and OFA fuel designs (see Table 1 on page 51 for fuel parameters).

2. Westinghouse 17x17 fuel assemblies stored in the middle of the 3x3 checkerboard contain uranium dioxide at a nxed nominal enrichment of 3.20 w/o :35 U over the entire length of each rod. Calculations show that at this enrichment, OFA fuel is more reactive with no soluble boron present.

3. Westinghouse 17x17 STD fuel assemblies surrounding the center of the 3x3 checkerboard contain uranium dioxide at a nominal enrichment of 1.48 w/o 235 U over the entire longth of each rod. Calculations show that at this enrichment, STANDARD fuel is more reactive with no soluble boron present. This arrangement of OFA surrounded by STD fuel in the 3x3 checkerboard configuration provides a conservative reactivity when compared to other fuel type configurations, including all OFA or all STD fuel.

4. The fuel pell-ts are modeled assuming nominal values for theoretical density and dishing fraction.

5. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

Criticality Analysis of Unit 2 3x3 Checkerboard 34

6. No credit is taken for ary 234 U or 236 U in the fuel, nor is any credit taken for the buildup of fission product poison material.

7. No credit is taken for any spacer grids or spacer sleeves.

8. No credit is taken for any bumable absorber in the fuel rods.

9 No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

10. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm/cm3 is used.

11. The array is infinite in the lateral (x and y) extent and finite in the axial (vertical) extent.

12. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 3x3 checkerboard arrangement as shown in Figure 7 on page 70.

With the above assumptions, the KENO-Va calculations of Keg under nominal conditions resulted in a K eg of 0.96865, as shown in Table 10 on page 60.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 1.0 Ke glimit. The following biases were included:

31ethodology: The benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias detennined in PHOENIX-P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack 3x3 checkerboard configuration, UO2material tolerances were

, considered along with construction tolerances related to the cell 1.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO-Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235 U Enrichment: The standard DOE enrichment tolerance of 0.05 w/o 235U about the nomiaal reference enrichment of 3.20 w/o 235 U for the center assembly and 1.48 w/o 235 U for the surrounding assemblies was considered.

UO 2Density: A 2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Criticality Analysis of Unit 2 3x3 Checkerboard 35

Storat:e Cell 1.D.: The :0.030 inch tolerance about the nominal 8.75 inch reference cell 1.D.

was considered.

Stora;;e Cell Pitch: The 0.040 inch tolerance about the cell pitch of 10.306 inches was assumed (see Section 1.1 for discussion of the cell pitch assumedt Stainless Steel Wall Thickness: The 0.005 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Consenative calculations show that an increase in reactivity can occur if the comers of four adjacent fuel assemblies are positioned together. This reactivity increase was considered.

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the KENO Va nominal reference K,g was considered.

Methodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse KENO Va methodology was -

considered.

The 95/95 K,gis developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO-Va reference reactivity.

The summation is shown in Table 10 on page 60 and results in a 95/95 Ke g of 0.99911.

Since Kegis less than 1.0, the Vogtle Unit 2 spent fuel racks will remain subcritical when cells are loaded in a 3x3 checkerboard with a 3.20 w/o 235 U 17x17 fuel assembly surrounded by 1,48 w/o i 235 U 17x17 fuel assemblies and no soluble boron is present in the spent fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties.

9.2 Soluble Boron Credit Keg Calculations To determine the amount of soluble boron required to maintain K,g s 0.95, KENO-Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal 1GNO-Va reference reactivity.

The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for 3x3 checkerboard storage in the Vogtle Unit 2 spent fuel racks are similar to those in Section 9.1 except for assumptions 2 and 10. Assumption 2 is different since the limiting fuel type for the center assembly of the 3x3 configuration with 200 ppm soluble boron is STANDARD fuel.

Assumption 10 is different since the moderator is replaced with water containing 200 ppm soluble boron. The all STD fuel case in the 3x3 checkerboard configuration provides a conservative reactivity when compared to other fuel type configurations with 200 ppm soluble boron.

Criticality Analysis of Unit 2 3x3 Checkerboard 36

With the above assumptions, the RENO.Va calculation for the nominal case results in a K,g of 0.90946, as shown in Table 10 on page 60.

l Temperature and methodology biases must be considered in the final K,g surmnation prior to comparing against the 0.95 Ke glimit. The following biases were included:

.ilethodology: The benchmarking bias as determined for the Westinghouse KENO.Va methodology was considered.

Water Temperature: A reactivity bias determined in PflOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50'F to 185'F).

To evaluate the reactivity efTects ' of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack 3x3 checkerboard configuration, UO2material tolerances were considered along with construction tolerances related to the cell 1.D., stoinge cell pitch, and stainless steel wall thickness. Uncenainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K,gis developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO-Va reference reactivity.

The summation is shown in Table 10 on page 60 and results in a 95/95 K,gof 0.94047.

Since Kegis less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for the 3x3 checkerboard storage configuration of 17x17 fuel assemblies in the Vogtle Unit 2 spent fuel racks when cells are loaded in a 3x3 checkerboard with a 3.20 w/o :35 U 17x17 fuel assembly surrounded by 1.48 w/o 235 U 17x17 fuel assemblies including the presence of 200 ppm soluble boron.

9.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial emichments higher than 1.48 w/o 235U in the peripheral cells of the 3x3 checkerboard in the Vogtle Unit 2 spent fuel racks is achievable by means of bumup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For burnup credit, a series of reactivity calculations is performed to generate a set of enrichment-fuel assembly discharge burnup ordered pairs which all yield an equivalent K,g when stored in the spent fuel storage racks.

Figure 10 on page 73 shows the constant Ke g contours generated for peripheral cells of the 3x3 checkerboard in the Vogtle Unit 2 spent fuei racks._ - The curve of Figure 10 represents ,

combinations of fuel enrichment and discharge burnup which yield the same rack multiplication factor (K eg) as compared to the rack leaded with 1.48 w/o :35U fuel assemblies at zero burnup in Criticality Analysis of Unit 2 3x3 Checkerboard 37

l peripheral cell locations of a 3x3 checkerboard. The 17x17 STD fuel assembly design provides a '

conservative reactivity relative to the 17x17 OFA design at all enrichment and bumup combinations shown in Figure 10 for the curve.

Uncenainties associated with bumup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD!MTU applied linearly to the burnup credit requirement to account for calculation and depletion uncertainties and 5% on the calculated bumup to account for bumup measurement uncertainty. The amount of additional soluble boron needed to account for these uncertainties in the bumup requirement of Figure 10 was 300 ppm. This is additional boron above the 200 ppm required in Section 9.2. This results in a total soluble boron requirement of 500 ppm.

It is imponant to recognize that the curve in Figure 10 is based on calculations of constant rack reactivity, in this way, the environment of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 10 are also provided in Table 7 on page 57. Use oflinear interpolation between the tabulated values is acceptable since the curve shown in Figure 8 is approximately linear between the tabulated points.

Previous evaluations have been performed to quantify axial bumup reactivity etrects and to confirm that the reactivity equivalencing methodology described in Reference I results in calculations of conservative burnup credit limits. The effect of axial burnup distribution on assembly reactivity has thus been addressed in the development of the Vogtle Unit 2 3x3 checkerboard bumup credit limit.

9.4 IFBA Credit Reactivity Equivalencing Storage of fresh fuel assemblies with nominal enrichments greater than 3.20 w/o 235 U in the middle cell of the 3x3 checkerboard in the Vogtle Unit 2 spent fuel storage racks is achievable by means of IFBA credit using reactivity equivalencing. Reactivity equivalencing with IFBA is predicated upon the reactivity decrease associated with the addition of Integral Fuel Bumable Absorbers. IFBAs consist of neutron absorbing material applied as a thin zirconium diboride (ZrB 2) coating on the outside of the UO2fuel pellet. As a result, the neutron absorbing material is a non-removable or integral part of the fuel assembly once it is manufactured.

A series at reactivity. calculations are perfonned to generate a set ofIFBA rod number versus enrichment ordered pairs which all yield the equivalent Kg when the fuel is stored in the middle of the 3x3 checketboard in the Vogtle Unit 2 spent fuel racks. The following assumptions are used for the IFBA rod assemblies in the PHOENIX-P models:

1.- The fuel assembly parameters relevant to the criticality analysis are based on the Westing-house 17xl_7 OFA design (see Table 1 on page 51 for fuel parameters). IFBA credit calcula-tions using the OFA design will bound the requirements for the STD design.

2. The fuel assembly is modeled at its most reactive point in life.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing frac-tion.

Criticality Analysis of Unit 2 3x3 Checkerboard 38

i

4. No credit is taken for any natural enrichment or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

23d 5 No credit is taken for any U or 23%) in the fuel, nor is any credit taken for the buildup of

- fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

! 7. NominalIFBA rod 10B loadings of 1.50 milligrams10B perinch (1.0X),1.875 milligrams 10B '

< per inch (1.25X) and 2.25 milligrams IDB per inch (1.5X) are used in determining the IFBA requirement.

8. The IFBA .10B loading was reduced by 16.67% to conservatively model a minimum poison length of 120 inches.

9. The moderator was pure water (no boron) at a temperature of 68'F with a density of 1.0 gm/cm3.

10. The array is infinite in the lateral (x and y) and axial (vertical) extent. This precludes any neu-tron leakage from the array.

I1. Standard Nestinghouse IFBA patterns (including previous standard patterns) for 17x17 fuel assembliesbete considered.

Figure 11 on page 74 shows the IFBA requirements for center assembly enrichments greater than 3.20 w/o 235 U that result in equivalent rack reactivity for the Vogtle Unit 2 3x3 checkerboard spent fuel rack configuration.- The data in Figure 11 is also provided on Table i1 on page 61 for ;

1.0X,1.25X and 1.5X IFBA loadings.

It is important to recognize that the curves ~in Figure 11.are based on reactivity equivalence calculations for the specific enrichment and IFBA combinations in actual rack geometry (and not just on simple comparisons of individual fuel assembly infinite multiplication factors). In this way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered.

Uncertainties associated with IFBA credit include a 5% manufacturing tolerance and a 10%

calculational uncertainty on theIDB loading of the IFBA rods. The amount of additional soluble boron needed to account for these uncertainties in the IFBA credit requirement of Figure 11 is bounded by the 300 ppm required for burnup credit in the 3x3 checkerboard in the Vogtle Unit 2 spent fuel racks. Therefore, the total soluble boron credit required for the 3x3 checkerboard in the Vogtle Unit 2 spent fuel racks remains at 500 ppm.

9.4.1 Infinite Multiplication Factor 2

The infinite multiplication factor, K., is used as a reference criticality reactivity point, and offers an alternative method for determining the acceptability of fuel assembly storage in the middle cell of the Vogtle Unit 2 3x3 checkerboard spent fuel racks. The fuel assembly K2 calculations are performed using PHOENIX-P. The following assumptions are used to develop the infinite multiplication factor model:

Criticality Analysis of Unit 2 3x3 Checkerboard 39 k

1. The fuel assembly is modeled at its most reactive point in life and no credit is taken for any burnable absorbers in the assembly.

2. The fuel rods are Westinghouse 17x17 OFA at an enrichment of 3.20 w/o 235 U over the infi-nite length of each rod (this is the maximum nominal enrichment that can be placed in the middle cell of the spent fuel racks for the 3x3 checkerboard configuration without IFBA rods).

3. The fuel array model is based on a unit assembly configuration (infmite in the lateral and axial extents)in Vogtle Unit 2 reactor geometry (no rack).

4. The moderator is pure water (no boron) at a temperature of 68'F with a density of 1.0 gm/cm3.

Calculation of the infmite multiplication factor results in a reference b of 1.410. This includes a 1% AK reactivity bias to conservatively account for calculational uncertainties. This bias is consistent with the standard conservatism included in the Vogtle Unit 2 core design refueling shutdown margin calculations. All fuel assemblies placed in the spent fuel racks must comply with the enrichment versus number ofIFBA rods curves in Figure 11 or have a reactivity less than or equal to the above value. Meeting either of these conditions assures that the maximum spent fuel rack reactivity will then be less than or equal to 0.95.

b Criticality Analysis of Unit 2 3x3 Checkerboard 40

l 10.0 Fuel . Rod Storage Canister Criticality A criticality analysisW was performed for the Fuel Rod Storage Canister (FRSC) which was provided to Vogtle. This report compared the FRSC, loaded with 5.0 w/o 235 U fuel rods, to an intact assembly with 5.0 w/o 235

~

U fuel rods. The conclusion was that the FRSC is less reactive than an assembly with 5.0 wio 235 U fuel rods. However, this analysis was done independent of any rack geometry. Therefore, for storage of the FRSC in the racks, the FRSC must be treated as ifit were an assembly with enrichment and burnup of the rod in the canister with the most limiting combination of enrichment and burnup.

Fuel Rod Storage Canister Criticality 41

11.0 Discussion of Postulated Accidents Most accident conditions will not result in an increase in Kg of the rack. Examples are:

Fuel assembly drop The rack structure pertinent for criticality is not excessively deformed, on top of rack and the dropped assembly which comes to rest horizontally on top of the rack has sufficient water separating it from the active fuel height of stored assemblies to preclude neutronic interaction.

Fuel assembly drop Typicaliy, the design of the spent fuel racks and fuel handling between rack equipment is such that it precludes the insertion of a fuel assembly in modules or between other than prescribed locations. However, in cases where this is not

[ rack modules and tme, the reactivity increase caused by this accident is bounded by the spent fuel pool wall misplacement of a fuel assembly inside the spent fuel racks.

However, three accidents can be postulated for each storage configuration which can increase 3

reactivity beyond the analyzed condition. The first postulated accident would be a change in the j spent fuel pool water temperature outside the normal operating range. The second accident would be dropping an assembly into an already loaded cell and the third would be a misload of an i

assembly into a cell for which the restrictions on location, enrichment, or burnup are not satisfied.

All accident conditions are analyzed without the presence of Boraflex neutron absorbing panels.

For the change in spent fuel pool water temperature accident, a temperature range of 32*F to 240*F is considered. Calculations were performed for all- Vogtle Unit I and 2 storage configurations to determine the reactivity change caused by a change in the Vogtle Units 1 and 2 spent fuel pool water temperature outside the normal range (50*F to 185'F). The results of these calculations are tabulated in Table 12 on page 62.

For the accident of dropping of a fuel assembly into an already loaded cell, the upward axial ,

leakage of that cell will be reduced, however the overall etTect on the rack reactivity will be insignificant. This is because the total axial leakage in both the upward and downward directions for the entire spent fuel array is worth about 0.003 AK. Thus, minimizing the upward-only leakage ofjust a single cell will not cause any significant increase in rack reactivity. Furthermore,

the neutronic coupling between the dropped assembly and the already loaded assembly will be low due to several inches of assembly nozzle structure which would separate the active fuel

regions. Therefore, this accident would be bounded by the misload accident.

For the assembly mistoad accident, calculations were performed to show the largest reactivity increase caused by a 5.00 w/o Westinghouse 17x17 STD or OFA unirradiated fuel assembly rnisplaced iroo a storage cell for which the restrictions on location, enrichment, or burnup are not satisfied. The raults of these calculations are also tabulated in Table 12.

~ For an occurrence of the above postulated accident conditions, the double contingency principle of ANSl!ANS 8.1-1983 can be applied. This states that one is not required to assume two unlikely, independent, concurrent events to ensure protection against a criticality accident. Thus, for these postulated accident conditior,s, the presence of additional soluble boron in the storage Discussion of Postulated Accidents 42 o______...__

1 1

. pool water (above the concentration required for normal conditions and reactivity equivalencing) can be assumed as a realistic initial condition since not assuming its presence would be a second unlikely event.

The amount of soluble bcron required to otiset each of the postulated accidents was determined with PHOESIX-P calculations, where the impact of the reactivity equivalencing methodologies on the soluble boron is appropriately taken into account. The additional amount of soluble boron for accident conditions needed beyond the required boron for uncertainties and burnup is shown in Table 12.

Discussion of Postulated Accidents 43

12,0 Soluble Boron Credit Summary Spent fuel pool soluble boron has been ured in this criticality analysis to offset storage rack and fuel assembly tolerances, calculational uncertainties, uncensinty associated with reactivity equivalencing (burnup credit and IFBA credit) and the reactivity increase caused by postulated accident conditions. The total soluble boron concentration required to be maintained in the spent fuel pool is a summation of each of these components. Table 13 on page 63 summarizes the storage configurations and corresponding soluble boron credit requirements.

Based en the above discussion, Kg will be maintained less than or equal to 0.95 for all considered configurations due to the presence of at least 1150 ppm soluble boron in the Vogtle Unit I spent fuel pool water and 1250 ppm in the Vogtle Unit 2 spent fuel pool water.

l l

i Soluble Boron Credit Summary 44 l l

_ __ _j

13.0 Storage Configuration Interface Requirements.

- The Vogtle _ Units 1 and 2 spent fuel pools have been analyzed for all cell storage, where all cells share the :ame storage requirements and limits, and several checkerboard storage configurations, where neighboring cells have different requirements and limits.

The boundary betw en ditTerent' empty cell checkerboard zones and the boundary between an empty cell checkerboard zone and an all cell storage zone must be controlled to prevent an undesirable increase in reactivity. This is accomplished by examining all possible 2x2 matrices of rack cells near the boundary (within the first few rows of the boundary) and ensuring that each of these 2x2 matrices conforms to checkerboard restrictions for the given region (or for 1 of the 2 regions if the 2x2 matrix of rack cells crosses over the interface boundary).

For example, consider a fuel assembly location E in the following matrix of storage cells.

1 A B C D E F G H I j Four 2x2 matrices of storage cells which include storage cell E are created in the above figure, They include (A,B,D,E), (B,C,E,F), (E,F,H,1), and (D,E,G,H). Each of these 2x2 matrices of storage cells is required to meet the checkerboard requirements determined for the given region.

The boundary between the 3x3 checkerboard zone and the empty cell checkerboard zones must be controlled to prevent an undesirable increase in reactivity. This is accomplished by examining all possible 3x3 matrices of rack cells which include a highly enriched assembly or equivalent from the 3x3 checkerboard configuration and ensuring that each of these 3x3 matrices conforms to restrictions for the 3x3 checkerboard (e.g. only 1 out of 9 assemblies may be at the high 35 enriclunent (3.20 w/o U - Unit 2 only) or equivalent for the 3x3 checkerboard configuration]. ;

However, on the empty cell checkerborad side of the boundary _only,2x2 matrices of rack cells near the boundary (within the first few rows of the boundary) should be reviewed to ensee that the empty cell checkerboard restrictions are met.

The boimdary between the 3x3 checkerboard zone and the all cell storage zone must be contr alled to prevent an undesirable increase in reactivity. This is accomplished by examining all pos sible 3x3 matrices of rack cells which include a highly enriched assembly or equivalent from th : 3x3 checkerboard configuration and ensuring that each of these 3x3 matrices conforms to restrictions for the 3x3 checkerboard (e.g. only I out of 9 assemblies may be at the high enrichment (. .20 w/o 35 U - Unit 2 only) or equivalent for the 3x3 checkerboard configuration]. The low enric hment of the 3x3 checkerboard configuration meets the requirements for storage in the all c,:11 region, and thus, placement of the low enrichment assemblies or equivalent from be 3x3 checkerboard configuration on the all cell side of the boundary will meet the criticality limits of these analyses.

Storage Configuration Interface Requirements 45 t

13.1 Interface Requirements within Vogtle Racks The following discussion of interface requirements illustrates example configurations that demonstrate the interface requirements discussed in Section 13.0 which are applicable to the Vogtle Units 1 and 2 Spent Fuel Racks:

All Cell Storage Next to The boundary between all cell storage and 3 out-of-4 storage 3-out-of-4 Storage can be either separated by a vacant row of cells or the interface must be configured such that the first row of cells afier the boundary in the 3-out-of-4 storage region uses attemating empty cells and cells containing assemblies at the 3-out-of-4 configuration enriclunent (2.45 w/o 235 U for Unit 1,2.40 w/o l 235 U for Unit 2) or equivalent. Figure 12 on page 75 illustrates the configuration at the boundary.

All Cell Storage Next to The boundary between all cell storage and 2-out of-4 storage i 2-out-of-4 Storage can be either separated by a vacant row of cells or the interface must be configured such that the first row of cells after the boundary in the 2-out-of 4 storage region uses alternating empty cells and cells containing assemblic.s at the 3-out-of-4 configuration enrichment (2.45 w/o 235 U for Unit 1,2.40 w/o 235 U for Unit 2) or equivalent. Figure 12 on page 75 illustrates the configuration at the boundary.

I 2-out-of-4 Storage Next to The boundary between 2-out-of-4 storage and 3 out-of-4 3-out-of-4 Storage storage can be either separated by a vacant row of cells or the interface must be configured such that the first row of cells after the boundary in the 3-out-of-4 storage region contain alternating empty cells and cells containing fuel assemblies at the 3-out-of-4 enrichment (2.45 w/o 235U for Unit 1,2.40 w/o 235 U for Unit 2) or equivalent. Figure 13 on page 76 illustrates the configuration at the boundary.

All Cell Storage Next to The boundary between all cell storage and 3x3 checkerboard 3x3 Checkerboard Storage storage can be either separated by a vacant row of cells or the (Unit 2 only) interface must be configured such that the first row of cells after the boundary in the all cell storage region uses the enriclunent of the low enrichment assemblies (1.48 w/o 235 U) of the 3x3 checkerboard configuration- or equivalent. Figure 14 on page 77 illustrates the configuration at the boundary.

Storage Configuration Interface Requirements 46

3-out-of-4 Storage Next to The boundary between 3 out of-4 storage and 3x3 3x3 Checkerboard Storage checkerboard storage can be either separated by a vacant row of (Unit 2 only) cells or the interface must be configured such that the first row of cells after the boundary in the 3-out-of-4 storage region contain w/o 235 the enrichment of the low enrichment assemblics (1.48 U) of the 3x3 checkerboard configuration or equivalent.

The second row of cells after the boundary in the 3-out of-4 storage region should contain alternating empty cells and cells containing fuel assemblies at the 3-out-of 4 enrichment (2.40 w/o 235 U) or equivalent. Figure 15 on page 78 illustrates the configuration at the boundary.

2-out-of-4 Storage Next to The boundary between 2 out of-4 storage and 3x3 3x3 Checkerboard Storage checkerboard storage can be either separated by a vacant row of

, (Unit 2 Only) cells or the interface must be configured such that the first row of cells after the boundary in the 2-out-of-4 storage region contain w/o 235 the enrichment of the low enrichment assemblies (1.48 U) of the 3x3 checkerboard configuration or equivalent.

The second row of cells after the boundary in the 2-out-of-4 storage region contain alternating empty cells and cells containing fuel assemblies at the 3-out-of-4 enrichment (2.40 w/o 235 U) or equivalent. Figure 15 on page 78 illustrates the configuration at the boundary.

Open Water Cells For all configurations at Vogtle Units I and 2, an open water cell is permitted in any location of the spent fuel pool to replace an assembly since the water cell will not cause any increase in reactivity in the spent fuel pool.

Non-Assembly For all configurations at Vogtle Units I and 2, non assembly Components components may be stored in open cells of the spent fuel pool provided at least one row of empty cells separates the components from the stored fuel.

Neutron Source and The placement 9f a neutron source or Rod Cluster Control RCCA in a Cell Assemblies (RCCA) will not cause any increase in reactivity in the spent fuel pool because the neutron source and RCCA are absorbers which reduce reactivity. Therefore, neutron sources and RCCA may be stored in an empty cell or in an assembly.

Non-Fuel Bearing Non-Fuel Bearing Assembly components (i.e. thimble plugs, Assembly Components Wet Annular Bumable Absorbers, etc.) may be stored in assemblies without affecting the storage requirements of that assembly.

Storage Configuration Interface Requirements 47

14.0 Summary of Criticality Results For the storage of Westinghouse 17x17 fuel assemblies in the Vogtle Units 1 and 2 spent fuel storage racks, the acceptance criteria for criticality requires the etTective neutron multiplication factor, K,g, to be less than 1.0 under No Soluble Boron 95/95 conditions, and less than or equal to

' 0.95 including uncenainties, tolerances, and accident conditions in the presence of spent fuel pool soluble boron. This repon shows that the acceptance criteria for criticality is met for the Vogtle Units 1 and 2 spent fuel racks for the storage of Westinghouse 17x17 fuel assemblies under both normal and accident conditions with soluble boron credit and the following storage configurations and enrichment limits:

Unit 1 Enrichment Limits All Cell Storage Storage of 17x17 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1.79 w/o 235 U or satisfy a minimum bumup requirement for higher initial enrichments. The soluble boron concentration that results in a K,g of less than 0.95 was calculated as 450 ppm. Including

'- accidents, the soluble boron credit required for this storage configuration is 950 ppm.

3-out-of-4 Storage of 17x17 fuel assemblies in a 3-out-of 4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an initial Storage nominal enrichment no greater than 2.45 w/o 235U or satisfy a minimum burnup requirement for higher initial enrichments. A 3-out of-4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble boron concentration that results in a K,g of less than 0.95 was calculated as 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 950 ppm.

2-out-of-4 Storage of- 17x17 fuel assemblies in a 2-out of-4 checkerbo-Checkerboard arrangement with empty cells. Fuel assemblies must have an ' 4.

Storage nominal enrichment no greater than 5.00 w/o 235 U. > ' of-4 checkerboard with empty cells means that no 2 fuw < nolies may be stored face adjacent. Fuel assemblies may be stored corner adjacent. The soluble boron concentration that results in a K,g of less than 0.95 was calculated as 100 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1150 ppm.

Summary of Criticality Results 48 i

Unit 21:adchment Limits All Cell Storage Storage of 17x17 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1.77 w/o 235 U or satisfy a minimum bumup requirement for higher initial enrichments. The soluble boron concentration that results in a Kegofless than 0.95 was calculated as 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 850 ppm.

3-ou t-o f-4 Storage of 17x17 fuel assemblies in a 3 out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies m,ust have an initial Storage nominal enrichment no greater than 2.40 w/o "35U or satisfy a minimum burnup requirement for higher initial enrichments. A 3-out-of-4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble baron concentration that results in a Ke g ofless than 0.95 was calculated as 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1050 pm.

2-o ut-of-4 Storage of 17x17 fuel assemblies in a 2-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an initial Storage nominal enrichment no greater than 5.00 w/o 235 U. A 2-out-of-4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent. Fuel assemblies may be stored comer adjacent. The soluble boron concentration that results in a Ke g of less than 0.95 was calculated as 50 ppi. h.:luding accidents, the soluble boron credit required for this storage configuration is 1250 ppm.

3x3 Checkerboard Storage of Westinghouse 17x17 fuel assemblies with nominal Storage enrichments no greater than 3.20 w/o 235 U (up to 5.00 w/o 235 U with IFBA credit)in the center of a 3x3 checkerboard. The surrounding fuel assemblies must have an initial nominal enrichment no greater than 1,48 w/o 235 U or satisfy a minimum bumup requirement for higher initial enrichments. Altematively, the center (high enrichment) cell of the 3x3 checkerboard may be loaded with any assembly which meets a maximum infinite multiplication factor (K z) value of 1.410 at cold reactor core conditions.The soluble boron concentration that results in a Ke g of less than 0.95 was calculated as 500 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1050 ppm.

Vogtle Units 1 and 2 Spent Fuel Racks 49

l 4

" The analytical methods employed herein conform with ANSI N18.2-1973, " Nuclear Safety Criteria for the Design of Stationary Pressurized Water Reactor Plants " Section 5.7 Fuel Handling System; ANSI

$7.2-1983. " Design Objectives for LWR Spent Fuel Storage Facilities at Nuclear Power Stations," )

' Section 6.4.2; ANSI N16.9-1975, " Validation of Calculational Methods for Nuclear Criticality Safety":

and the NRC Standard Review Plan, Section 9.1.2, " Spent Fuel Storage '.

4 i

i 4

l l

l i

J p i

i i

1 8

i i

i t

) ,

Vogtle Units 1 and 2 Spent Fuel Racks 50

- . . . ._. - - _ - =_ _ _ . - . - . - - - - . . - .

Table 1. Nominal Fuel Parameters Employed in the Criticality Analysis Westinghouse Westinghouse Paratneter 17x17 STD 17x17 OFA j Number of Fuel Rods per Assembly 264 264 Fuel Rod Clad O.D. (inch) 0.3740 0.3600 Clad Thickness (inch) 0.0225 0.0225 Fuel Pellet O.D. (inch) 0.3225 0.3088 Fuel Pellet Density (% of Theoretical) 95 95-Fuel Pellet Dishing Factor (%) 1.2074 1.2110

, Rod Pitch (inch) 0.496 0.496 Number of Guide Tubes 24 24 Guide Tube O.D. (inch) 0.482 0.474 Guide Tube Thickness (inch) 0.016 0.016 Number ofInstrument Tubes 1 1 Instrument Tube O.D. (inch) 0.482 0.474 Instmment Tube Thickness (inch) 0.016 0.016 Vogtle Units 1 and 2 Spent Fuel Racks - 51

I Table 2. All Cell Storage 95/95 K ett for Vogtle Unit i No Soluble Soluble Boron Boron Credit Nominal KENO-Ya Reference Reactivity: 0.94250 0.88054 Calculational & Methodology Blases:

Methodology (Benchmark) Bias 0.00770 0.00770 i Pool Temperature Bias (50'F - 185'F) 0.00986 0.00915 TOTAL Bias 0.01756 0.01685 Tolerances & Uncertaintles:

UO2Enrichment Tolerance 0.00860 0.00859 UO2DensityTolerance 0.00331 0.00377 Fuel Pellet Dishing Variation 0.00170 0.00198 i Cell Inner Dimension 0.00000 0.00003 Cell Pitch 0.03421 0.03464 Cell Wall Thickness 0.00972 0.00695 Asymmetric Assembly Position 0.00789 0.00551 Calculational Uncertainty (95/95) 0.00178 0.00177 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.03778 0.03718 f9 Tj ((tolerance,...or...uncertaintyg)2) h-i Final K,g Including Uncertainties & Tolerances: 0.99784 0.93457 Vogtle Units 1 and 2 Spent Fuel Racks 52

1 Table 3. Minimum Burnup Requirements for Vogtle Unit 1 3-ou t-of-4 2-out of-4 En chn ent Br ec erboard G eckerboard 235 B (w/o U) (MWD /MTU) gg\yD/%1TU) (M\YD/A 'U) 1.79 0 0 0 2.00 3879 0 0 2.20 7001 0 0 2.40 9712 0 0' 2.45 10342 0 0 2.60 12140 1488 0 2.80 14391 3415 0 3.00 16550 5282 0 3.20 18684 7097 0 3.40 20838 8866 0 3.60 23039 10597 0 3.80 25292 12296 0 4.00 27584 13972 0 4.20 29880 15630 0 4.40 32127 17279 0 4.60 34250 18924 0 4.80 36155 20574 0 5,00 37728 22235 0 Vogtle Units I and 2 Spent Fuel Racks 53

Table 4,3 out-of-4 Checkerboard 95/95 K,rr for Vogtle Unit 1 4-No Soluble Soluble Boron Boron Credit Nominal KENO Va Reference Reactivity: 0.95418 0.89720 Calculational & Methodology Blases:

d

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 185'F) 0.00578 0.00513 TOTAL Bias 0.01348 0.01283

-Tolerances & Uncertaintles:

UO2Enrichment Tolerance 0.00505 0.00513 UO2Density Tolerance 0.00281 0.00325 Fuel Pellet Dishing Variation 0.00165 0.00190 4

Cell Inner Dimension 0.00002 0.00000 Cell Pitch 0.02486 0.02553 Cell Wall Thickness 0.00846 0.00591

Asymmetric Assembly Position 0.00720 0.00542 Calculational Uncertainty (95/95) 0.00200 0.00200 j Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.02812 0.02774 t9

[ ((tolerance, . . . or. . .uncertaintyg)2 )

t=1 Final Kert Including Uncertainties & Tolerances: 0.99578 0.93777 i

Vogtle Units 1 and 2 Spent Fuel Racks 54

i Table 5. 2-out-of-4 Checkerboard 95/95 K,rg for Vogtle Unit I t

No Soluble Soluble Boron i Boron Credit Sominal KENO Va Reference Reactivity: 0.93670 0.92077 I

Calculational & Methodology Blases:

Methodology (Benchmark) Bias 0.00770 0,00770 Pool Temperature Bias (50*F - 185'F) 0.00026 0.00013 TOTAL Bias 0.00796 0.00783 Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.00152 0.00158 UO 2DensityTolerance 0.00229 0.00248 Fuel Pellet Dishing Variation 0.00138 0.00139 CellInner Dimension 0.00001 0.00005 Cell Pitch 0.00597 0.00599 Cell Wall Thickness 0.00509 0.00406 Asymmetric Assembly Position 0.00873 0.00420 Calculational Uncertainty (95/95) 0.00253 0.00233 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01275 0.00975 I9 T

_ ((tolerance ...or...

s uncertainty,)2) i8 I Final K en Including Uncertainties & Tolerances: 0.95741 0.93835 Vogtle Units 1 and 2 Spent Fuel Racks 55

Table 6. All Cell Storage 95/95 Ke n for Vogtle Unit 2 No Soluble Soluble Boron Boron Credit Nominal KENO Va Reference Reactivity: 0.96819 0.92003 Calculational & Methodology Blases:

Methodology (Benchmark) Bias 0.00770 0.00770

( Pool Temperature Bias (50'F 185'F) 0.00915 0.00913 TOTAL Bias 0.01685 0.01683 Tolerances & Uncertainties:

UO 2Enrichment Tolerance 0.00898 0.00899 UO2DensityTolerance 0.00334 0.00362 Fuel Pellet Dishing Variation 0.00175 0.00188

( Cell Inner Dimension 0.00019 0.00007 Cell Pitch 0.00437 0.00436 Cell Wall Thickness 0,00331 0.00263 Asymmetric Assembly Position 0.00664 0.00608 Calculational Uncertainty (95/95) 0.00180 0.00168 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01347 0.01312 I9

[ ((tolerance ...or...uncertaintyg)2) g

$i=I Final K,g Including Uncertainties & Tolerances: 0.99851 0.94998 Vogtle Units 1 and 2 Spent Fuel Racks 56 l........ -

m ,

Table 7. Minimum Burnup Requirements for Vogtle Unit 2 3-out-of-4 2-out-of-4 3x3 Enrich ent r Checkerboard Checkerboard Checkerboard (w/o 235 Burnup Burnup Burnup (*)

U) (MWD /MTU)

(MWD /MTU) (MWD /MTU) (MWD /MTU) 1.48 0 0 0 0 1.60 0 0 0 3223 1.77 0 0 0 7206 l

1.80 591 0 -0 7846 2.00 4182 0 0 11708 2.20 7268 0 0 14987 2.40 9980 0 0 17841 2.60 12431 2034 0 20406 2.80 14714 4000 0 22795 3.00 16908 5906 0 25101 3.20 19071 7758 0 27393 3.40 21246 9564 0 29720 3,60 23456 11329 0 32108 3.80 25706 13063 0 34561 4.00 27986 14770 0 37062 4.20 30265 16459 0 39571 4.40 32497 18136 0 42027 4.60 34617 19808 0 44347 4.80 36540 21483 0 46426 5.00 38168 23167 0 48136

(*) Burnup required on perip$ral fuel assemblies.

Vogtle Units I and 2 Spent Fuel Racks 57

Table 8. 3-out-of-4 Checkerboard 95/95 Ke n for Vogtle Unit 2 i

No Soluble Soluble Boron Boron Credit Nominal KENO-Va Reference Reactidty: 0.97240 0.91440 Calculational & Methodology Blases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Blas (50'F - 185'F) 0.00503 0.00493 TOTAL Bias 0.01273 0.01263 Tolerances & Uncertainties:

UO 2Enrichment Tolerance 0.00532 0.00544 UO Density Tolerance 0.00284 0.00328 Fuel Pellet Dishing Variation 0.00166 0.00190 Cell Inner Dimension 0.00013 0.00000 Cell Pitch 0.00315 0.00328 Cell Wall Thickness 0.00275 0.00199 Asymmetric Assembly Position 0.00453 0.00557 Calculational Uncertainty (95/95) 0.00206 0.00196 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Unnertainty (statistical) 0.00951 !01013

[ (( tolera n ce; . . . o r. . . un c erta in tyi)2) i=1 Final K,g Including Uncertainties & Tolerances: 0.99464 0.93716 Vogtle Unit . I and 2 Spent Fuel Racks 58

l Tuhle 9. 24:ut<>f-4 Checkerboard 95/95 K,tr for Vogtle Unit 2 1

No Soluble '

Soluble Horon Horon Credit Nominal KENO.Va Reference Reactivity: 0.94622 0.93390 l Calculational & Methodology Blasest ;

Methodology (Benchmark) Blas 0.00770 0.00770 l l Pool Temperature Ilias (50'F 185'F) 0.00031 0.00032 TOTAL 13ias 0.00801 0.00802 Tolera; ces & Uncertaintlest l UO Enrichment Tolerance 0.00150 0.00158 UO DensityTolerance 0.00227 0.00233 Fuel Pellet Dishing Variation 0.00140 0.00142 Cell Inner Dimension 0.00007 0.00006

! Cell Pitch 0.00075 0.00078 Cell Wall Thickness 0.00162 0.00152 Asytumetric Assembly Position 0.00369 0.00026 Calculational Uncertainty (95/95) 0.00250 0.00092 Methodology Blas Uncertainty (95/95) 0.00300. 0.00300 TOTAL Uncertainty (statistical) 0.00644 0.00545 i

I9

) [ ((tolerance,...or...uncertaintyg)2) bt Final K err including Uncertainties & Tolerances: 0.96067 0.94737

\

i 1

Vogtle Units i and 2 Spent Fuel Racks - 59

- - . ,_.--_-. , . - - . . .-.- - -._ - - - - . _ - . _ . _ . - - . . -.._ -

ML20217H912

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